1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a color liquid crystal display device for coloring a background or display regions in a single color or a plurality of colors.
2. Description of the Related Art
Conventionally, several schemes have been proposed for a single-color liquid crystal display device for coloring a background or display regions of the liquid crystal display device.
A first conventional example is a single-color liquid crystal display device having a color polarizing film disposed outside a liquid crystal display element. The device has a simple structure and is generally used in many applications.
A second conventional example is a single-color liquid crystal display device in which a dichroic dye is mixed in a nematic liquid crystal of a liquid crystal element to cause the dichroic dye to function with the operation of nematic liquid crystal molecules, which is called a guest-host scheme.
However, such conventional single-color liquid crystal display devices display characters or figures colored with a dye or a dichroic dye on a white background, or conversely, display white characters or figures on a background colored with a dye or a dichroic dye, resulting in a low contrast.
The above-described liquid crystal display devices also have a disadvantage of limited number of colors to be displayed due to a limited number of dyes or dichroic dyes available.
Thus, as a third conventional example, a single-color liquid crystal display device composed of a single polarizing film, a TN liquid crystal element having a twist angle of 90 degrees, a retardation film for circularly polarized light, a cholesteric liquid crystal film, and a light absorbing film has been proposed. The single-color liquid crystal display device displays brightly colored characters or figures on a black background utilizing a selective scattering phenomenon, or conversely, displays black characters or figures on a brightly colored background, thus obtaining display with a higher contrast.
Also, the single-color liquid crystal display device can display optional colors only by adjusting a twist pitch in the cholesteric liquid crystal film to thereby realize a display device for colorful single-color display.
Incidentally, such conventional arts are disclosed, for example, in Japanese Laid-open Patent Application No. 52-5550 and Japanese Laid-open Patent Application No. 6-230362.
However, the above-mentioned single-color liquid crystal display device using a cholesteric liquid crystal film has disadvantages in that the viewing angle characteristic is poor due to the use of a TN liquid crystal element and it is difficult to apply the device to a high density liquid crystal display device having 100 or more scanning lines.
Additionally, the above-mentioned device provides only single-color display since only one cholesteric liquid crystal film is used.
The device also has a disadvantage in that backlight illumination can not be utilized due to the use of a light absorbing film which does not transmit light, thereby reducing nighttime or low ambient light visibility.